Stack-jet curtain

ABSTRACT

An apparatus permitting observation of the true nature of effluent gas traversing a stack. The apparatus is instrumental in forming an air curtain around the outlet end of the stack where the exhaust gases traversing the stack are emitted from the restrictive closure of the stack to the atmosphere. An air curtain so produced creates a transparent barrier that separates the hot moisture bearing effluent gases of the stack from the cooler air of the surrounding atmosphere to delay cooling the gases passing up through the exhaust stack until they pass beyond the air curtain and are discharged to the atmosphere. Delay in cooling the effluent gas prevents it from condensing as visible clouds and thus permits observation at this point to present a true appearance of the effluent.

Q United States Patent 1 1 3,566,768

[ 72] Inventor Robert H. Walpole, Jr. FOREIGN PATENTS 820,619 11/1951 Germany 98/36 HP; r g 735,519 8/1955 Great 1311111111... 239/543 907,852 10 1962 Great Britain 98 58 [45] Patented Mar. 2, 1971 I [731 Assignee The Air Preheater Company, Inc. Primary Examiner-Lloyd L King w u n y Assistant Examiner-John J Love Attorneys--Wayne l-l. Lang and Eldon H. Luther [54] STACK-JET CURTAIN W 2 Claims, 2 Drawing Figs.

[52] US. Cl 98/58, ABSTRACT: An apparatus permitting observation f the true 239/l4 nature of effluent gas traversing a stack. The apparatus is in- [51] Int. Cl E041 17/02 smlmemal in f i an air cumin around the outlet end f Fleld ofseal'ch 58, the ta k where the exhaust ga es traversing the stack are 591 60; 110/184; 126/307; 239/2901 291154815491 emitted from the restrictive closure of the stack to the at- 55 (D1 55 (F)1 5581 21 mosphere. An air curtain so produced creates a transparent barrier that separates the hot moisture bearing efiluent gases [56] References cued of the stack from the cooler air of the surrounding atmosphere UNITED STATES PATENTS to delay cooling the gases passing up through the exhaust 1,381,030 6/1921 Thompson 239/5 58X stack until they pass beyond the air curtain and are discharged 2,901,033 8/1959 Holden 239/558X to the atmosphere. Delay in cooling the effluent gas prevents it 3,1 15,820 12/1963 Adelt 98/60 from condensing as visible clouds and thus permits 0bserva- 3,23 1 ,004 1/1966 Reed et a1 98/60X tion at this point to present a true appearance of the effluent.

[Fl-Z UE/VT .0; 1 l CO/VDE/VS/N 1 111113111 I zozvz M- f 1 1 I 1 A 11 11 1 1 1 zo/ve- 0F 51 1 1 1 1111 .1 1 1.1 1 111111 -08;VA770/V 111 1- 1 III I WIT/{OUT 1 1 aasneucr/o/v l 1 l 1 l6 1 I 1 l 25 I I l l r l l BACKGROUND OF THE INVENTION Operations such as combustion, evaporation, drying and gas scrubbing inherently contain water vapor in the efiluent that condenses when discharged to a colder atmosphere, forming opaque plumes. To a layman the presence of condensed moisture in the form of opaque plumes may appear a flagrant example of air polluting, and to an air pollution control observer a plume may disguise the true appearance of the particulate bearing noxious gas. Yet chemical analysis may show that 99.99 percent of the stack effluent content is harmless water vapor and clean air components. I

In many localities however, a contaminant is defined as any discharge of any material that creates an opaque plume as observed at the point of discharge to the atmosphere. Thus the condensation of harmless water vapor would by definition become a true contaminant.

Various methods of eliminating the condensed vapor plume from a stack exhaust have been proposed such as dilution with heated atmosphere air, superheating the effluent so that it disperses before condensation occurs, condensation by chilling the entrained moisture, or any combination of the above methods. However the costs of installation and operation of these methods for eliminating a harmless constituent are excessive and serve no purpose exceptto remove obscuring water vapor from the plume. Therefore this invention is directed to a minimum cost arrangement making possible valid observation of the true content of the exhaust gases at the point of discharge to the atmosphere thus making unnecessary alternate or further measures of effluent condensate suppression or elimination.

This invention thus relates to an arrangement for application to the exhaust stack of a device for an industrial or combustion process whereby hot, moisture laden gases being ex- ,hausted to the atmosphere are not permitted to immediately condense in the cooler atmosphere lying directly adjacent the outlet for the exhaust stack, but are instead directed through an invisible or transparent duct before being educted to the atmosphere whereby the effluent gases traversing the transparent duct may be observed in their true state.

One of the most universally used methods of measuring the degree of particulate contamination of a gas stream is a visual observation of its discharge at the point of release to the atmosphere known as its Ringleman rating. Such a rating is useless when conditions permit harmless moisture in the effluent gas to condense and cloud the true content thereof.

Therefore it is the chief objective of this invention to prevent the temperature of the effluent gas from dropping below its dew point for a controlled distance after it leaves the exhaust stack. Observation of the exhaust gas at this point will then produce a true appearance of the effluent.

Summary of the Invention With concern for cleaner environmental air conditions, restrictions are often required for the removal from the effluent gas contaminants including particulate matter and noxious gases carried by the effluent gas prior to its discharge to the atmosphere.

The arrangement of this invention provides a simple device for the addition to exhaust stacks permitting a true visual and measurable evaluation of the contamination present at the point of exhaust to the atmosphere. The arrangement provides a transparent air curtain at the outlet of the stack surrounding the effluent. This air curtain permits the observation therethrough of the effluent and its contents without the masking effect of clouds of condensate.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of a stack constructed according to the invention; and

FIG. 2 is a perspective view of a slightly modified form of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Looking now at FIG. 1 of the drawings the numeral 10 refers to a conventional exhaust duct or stack for one of many various industrial or combustion processes where hot, moist gases are exhausted to the atmosphere.

Surrounding the exhaust duct at its outlet end is a jacket 12 having an imperforate end plate 14 and a perforate end plate 16 adjacent the exhaust end of the duct which encloses a chamber 28. The annular end plate 14 lies adjacent to an inlet port 18 through which a supply of clean, dry compressed air is provided to the chamber 28 from any conventional source such as a compressor 22. The end plate 16 is apertured with elongate slots 24 whereby a supply of compressed air directed through port 18 intothe chamber 28 between the stack 10 and its jacket 12 is exhausted therefrom in the form of a curtain 25 of air continuous with the outlet end of the stack and substantially surrounding it.

When the compressed air or other fluid forming the curtain wall has a velocity equal to or greater than the air traversing the effluent zone it encompasses, a separating barrier is formed between it andthe environment external to the barrier. By controlling the moisture content of the fluid comprising the barrier curtain and maintaining it less than that of the discharging effluent it surrounds and less than that of the atmosphere adjacent thereto, conduction between the surrounding atmosphere and the effluent is minimized and condensation is eliminated. As the curtain fluid is dissipated by association with the environment its effectiveness as a separating barrier decreases. Therefore at some point removed from the jet curtain discharge openings, condensation of the effluent will occur. However in the zone of containment within the transparent air curtain the effluent will have a visual appearance unobscured by condensed water vapor and will permit unobstructed observation, for example, and a valid rating by a visual *Ringleman density scale grading, photoelectric cell or photographic grading. It will also permit general lay observation of the degree of particulate contamination otherwise impossible by intermixing with visible clouds of condensed water vapor and thus demonstrate to the public the true harmless nature of the effluent gas.

A modified form of the device is shown in FIG. 2 where a pipe is formed into a collar 26 which is adapted to tightly surround the stack 10. An inlet duct 18 is connected to a source 22 of clean, dry compressed air to supply air for the air curtain thereto while exhaust ports in the form a multiplicity of circular apertures 24-A exhaust air therefrom. The apertures 24-A are each positioned with their central axis substantially parallel to the central axis of the stack to exhaust the compressed air therefrom as a continuous curtain in the manner previously defined.

Under certain cases where the effluent gas is discharged into ambient atmosphere having the proper conditions of temperature, humidity, crosswind or other turbulence conditions conducive of aggravated condensation, the characteristics of the air for the curtain 25 may be varied. Thus the size of the outlets 24 may be varied and the output of the compressor 22 may be increased or decreased to vary the width of the air curtain 25. Similarly air from compressor 22 may be directed through a drier 32 and/or a heater 34 to supply air for the air curtain 25 .which is itself completely free of any characteristic enabling any moisture content thereof to condense and not permit the true observation of the exhaust gas.

Thus it is evident that the specific construction of the device disclosed and described herein is presented for the purpose of explanation and illustration only and is not intended to indicate the limits of the invention, the scope of which is defined only by the following claims.

I claim:

1. A stack for the discharge of hot exhaust gases to the cooler atmosphere comprising an open ended duct, a collar tain will form a transparent barrier intermediate the hot exhaust gases and the cooler atmosphere.

2. A stack for the discharge of exhaust gases in the manner defined in claim 1 including drying means in the passageway supplying compressed gas to the plenum chamber whereby moisture is removed from the compressed air before it is educted from the plenum chamber as a transparent extension of the end of the stack. 

1. A stack for the discharge of hot exhaust gases to the cooler atmosphere comprising an open ended duct, a collar surrounding the outlet end of the duct in spaced relation arranged to provide a plenum chamber therebetween, an inlet port in said chamber, a source of compressed air, a passageway directing a quantity of compressed air from its source to the inlet port of said chamber, heating means in the passageway supplying compressed air to said chamber, and means educting compressed air from said chamber in a pattern that comprises an air curtain as a transparent extension for the walls of the open ended duct whereupon said air curtain will form a transparent barrier intermediate the hot exhaust gases and the cooler atmosphere.
 2. A stack for the discharge of exhaust gases in the manner defined in claim 1 including drying means in the passageway supplying compressed gas to the plenum chamber whereby moisture is removed from the compressed air before it is educted from the plenum chamber as a transparent extension of the end of the stack. 